The compounds made by the instant process, because they are less basic than normal unsubstituted or N-alkyl substituted hindered amines, are particularly effective in the stabilization of polymer compositions where the activity of the more basic hindered amines is significantly reduced by interaction with the polymer substrate or additives in the polymer system. Examples of polyolefin compositions in which the instant compounds are particularly effective include thermoplastic polyolefins where pigment interactions with basic hindered amine stabilizers interfere with painting the substrate, in greenhouse films and agricultural where acidic residues from pesticides interfere with the activity of normal hindered amine stabilizers, and in flame retardant polyolefins where acidic residues from the decomposition of halogenated flame retardants deactivate normal more basic hindered amine stabilizers. Examples of automotive coatings compositions in which the instant compounds are effective include thermoset acrylic resins with melamine crosslinking agents as well as acrylic alkyd or polyester resins with isocyanate crosslinking agents and epoxy resins with carboxylic acid, anhydride or amine crosslinking agents.
The instant N-(hydroxyalkoxy) (NOROL) compounds are described in copending application Ser. No. 09/257,711.
U.S. Pat. No. 4,921,962 describes a process for the formation of N-hydrocarbyloxy derivatives of sterically hindered amines in which a hindered amine or N-oxyl substituted hindered amine is reacted with a hydrocarbon solvent in the presence of a hydroperoxide and a metal carbonyl, metal oxide or metal alkoxide catalyst. The instant process describes the synthesis of hindered amine compounds exclusively from alcohols whereas U.S. Pat. No. 4,921,962 is solely restricted to the use of hydrocarbon solvents. The process of U.S. Pat. No. 4,921,962 minimizes the amount of water left in the reaction mixture as a result of using commercially available aqueous hydroperoxide solutions. This is accomplished by azeotropic distillation with the hydrocarbon solvent, extraction of an aqueous hydroperoxide with hydrocarbon solvent or the use of a hydroperoxide with very low water content such as 90% tert-butyl hydroperoxide with contains only 5% water. The instant process does not teach the removal of water from the aqueous hydrogen peroxide or organic hydroperoxide used in the instant process. Water can even be used as a cosolvent in the instant process. Furthermore, the prior art process described in U.S. Pat. No. 4,921,962 specifically teaches the use of tertiary alkyl peroxides whereas hydrogen peroxide is the most preferred peroxide in the instant process. The preferred metal catalysts for the prior art process described in U.S. Pat. No. 4,921,962 are chromium trioxide and molybdenum catalysts whereas the preferred metal catalysts in the instant process are iron(II), iron(II), copper(I) and copper(II) salts or metal-ligand complexes.
U.S. Pat. No 5,374,729 describes a process for the preparation of N-methoxy derivatives of hindered amines from the reaction of the corresponding N-oxyl compound with methyl radicals produced by the combination of aqueous hydrogen peroxide and a peroxide-decomposing transition metal salt in the presence of dimethyl sulfoxide. The instant process involves the formation of alcohol substituted derivatives of the hindered amines.
4-Hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine and 4-oxo-1-oxyl-2,2,6,6-tetra-methylpiperidine have been used to trap carbon centered radicals formed from methanol, ethanol, 2-propanol and 2-methyl-2-propanol as reported by S. Nigam et al., J. Chem. Soc., Trans. Faraday Soc., 11976, (72), 2324 and by K.-D. Asmus et al., Int. J. Radiant. Biol., 1976, (29), 211. The carbon centered radical were produced by reaction of the specified alcohols with hydroxy radicals formed by the reaction of hydrated high energy electrons with nitrous oxide. The instant process is clearly distinct from these prior art disclosures.
D. H. R. Barton et al., Tetrahedron, 1996, (52), 10301 describe the formation of N-alkoxy-2,2,6,6-tetramethylpiperidine derivatives in the reaction of unactivated hydro-carbons with iron(II) and iron(III) species, hydrogen peroxide and various coadditives in the presence of N-oxyl-2,2,6,6-tetramethylpiperidine (TEMPO) even though some of the hydrocarbon solvent is oxidized to the corresponding alcohol in the reaction. Again, this article does not disclose or suggest the instant process.
The instant process provides a convenient method for the synthesis of a novel class of hindered amine stabilizer compounds as disclosed in copending application Ser. No. 09/257,711. These compounds, because of the presence of a polar alcohol functionality on the N-atom of the hindered amine ring, complement the relatively non-polar N-O-hydrocarbon hindered amine derivatives described in U.S. Pat. No. 5,204,473. The polar hydroxy group and the N-alkoxy moiety which reduces hindered amine basicity are introduced into the hindered amine moiety in one simple reaction.
The instant process also takes advantage of the compatibility of many alcohols with commercially available aqueous hydrogen peroxide and organic hydroperoxide solutions. The process also uses only catalytic quantities of a metal salt and does not require high temperatures.